Whisk the water and yeast together in a crock jar that is at least 1 gallon. You can also use the ceramic insert from a crock pot if you don’t have a jar. Just don’t store in metal!
Mix in the sugar and let set a couple minutes.
Stir in flour. The consistency should be just slightly thinner than a pancake batter. Adjust your water or flour if needed to reach desired consistency.
Drop in the potato. Cover with a cup towel. Stir about 6 hours in. The starter is ready to use in 12 hours, but I like to let it set about 24 hours before using for a more traditional sourdough flavor.